c# - Linq query from IEnumerable of integers -

i have logical problem within asp.net mvc project. i'm developing social media app looks facebook. got work except 1 thing.

the application has table called follow, contains loggedinuser_id , usertofollow_id. have ienumerable of integers contains list of userstofollow_id logged in user, method looks like:

public ienumerable<post> postsforflow(int userid, string username) {     ienumerable<int> usertofollowid = db.follow.where(a =>          a.loggedinuser.id == userid).select(b => b.usertofollow.id);       return null; } 

how foreach on integers of posts loggedinuser want follow?

can resolve linq query?

would work? assuming user has 1 many relationship posts:

public ienumerable<post> postsforflow(int userid) {     var useridstofollow = db.follow.where(a =>         a.loggedinuser.id == userid).select(b => b.usertofollow.id);      return db.users         .where(u => useridstofollow.contains(u.id))         .selectmany(u => u.posts); } 

edit

in order test this, since don't have database, made dummy classes mock yours. if these similar have, should work.

the user table, has id , list of post

public class user {     public int id { get; set; }     public list<post> posts { get; set; } } 

the post table, has text property (for testing)

public class post {     public string text { get; set; } } 

the follow table, has loggedinuser , usertofollow

public class follow {     public user loggedinuser { get; set; }     public user usertofollow { get; set; } } 

the 'db', contains list of user , list of follow (these tables)

public static class db {     public static list<follow> follow = new list<follow>();     public static list<user> users = new list<user>(); } 

then created method populate database 10 users. user id '0' "logged in user", , users 1 - 9 being followed user 0, , have 4 posts each

/// <summary> /// populates db 10 users. users /// 1 9 being followed user 0 /// </summary> public static void populatedb() {     // create logged in user     var loggedinuser = new user { id = 0, posts = new list<post>() };     db.users.add(loggedinuser);      // create 9 other users 4 posts each     (int = 1; < 10; i++)     {         var newuser = new user         {             id = i,             posts =                 new list<post>                 {                     new post {text = "post #" + i},                     new post {text = "post #" + (i * 10)},                     new post {text = "post #" + (i * 20)},                     new post {text = "post #" + (i * 30)}                 }         };          // add other user         db.users.add(newuser);          // have logged in user follow new user         db.follow.add(new follow { loggedinuser = loggedinuser,              usertofollow = newuser });     } } 

then, test out, call 2 methods:

public static void main() {     populatedb();     var postsforflow = postsforflow(0);      // postsforflow has 36 entries - 4 each     // of 9 users user '0' following     console.writeline(postsforflow.count());      // output: 36 (9 users * 4 posts each)      // now, test further, stop following users have ids     // leave 5 users: 1, 3, 5, 7, 9     foreach (var follow in db.follow         .where(f => f.usertofollow.id % 2 == 0)         .tolist())     {         db.follow.remove(follow);     }      postsforflow = postsforflow(0);     console.writeline(postsforflow.count());     // output: 20 (5 users * 4 posts each) }